(1) Field of the Invention
The present invention relates to an inspection device and an inspection method for inspecting a magnetic disk or a magnetic head, and in particular, to an inspection device and an inspection method capable of conducting the inspection with high accuracy even when the format of the servo pattern written on the magnetic disk varies.
(2) Description of the Related Art
Magnetic disks to which the servo pattern has previously been written by stamper technology and microscopic processing technology (e.g., nano-printing) for realizing high data density (DTM (Discrete Track Media), BPM (Bit Patterned Media), magnetic transfer media, etc.) are becoming the mainstream of the magnetic disks for HDDs (Hard Disk Drives) in recent years. An inspection device for inspecting a magnetic disk or a magnetic head is required to check whether the quality of the magnetic disk or magnetic head is good or not by reading and writing test data from/to data areas of the disk while demodulating the servo pattern written on the magnetic disk, suppressing the track deviation (deviation of the head from the intended track) caused by the wobbling of the disk surface, the eccentricity (decentering) of the disk, etc., and executing on-track servo control.
If a magnetic disk has an eccentricity, the read/write operation from/to the disk generally becomes unstable due to a fluctuation in the cycle of the clock signal reproduced from the magnetic disk. In the demodulation of the servo pattern, demodulation errors of position information (track code, sector code) and position signal detection errors increase in proportion to the magnitude of the eccentricity. To deal with this problem, JP-A-6-223502 has proposed a clock signal correction circuit comprising a voltage-controlled oscillator, storage means which stores signals corresponding to eccentricities of the disk, and correction means which changes the phase or the frequency of the clock signal outputted by the voltage-controlled oscillator according to the signal (corresponding to a certain eccentricity) stored in the storage means.
Further, the format of the servo pattern varies depending on the drive maker or the model of the drive even in the same drive maker. Therefore, correctly demodulating the servo pattern requires an inspection conducted by acquiring a special-purpose channel control IC corresponding to each servo pattern, which has involved problems of complicated and troublesome work and a cost rise. To address these problems, JP-A-2010-49775 has proposed a general-purpose servo demodulation circuit capable of dealing with a plurality of servo patterns by setting information in a part of the servo pattern (partial information) as a detection pattern, comparing a demodulated pattern of the partial information with the detection pattern, and controlling operation timing of the inspection according to the result of the comparison.